Lasers are commonly used to generate light. One type of laser includes a wave guided gain medium, collimating optics (collimator), and a plane diffraction grating, retroreflacting light, which together define an external cavity for the laser. This type of laser is commonly referred to as having a Littrow configuration. In this configuration, light generated by the gain medium is directed through the collimator at the diffraction grating, and the diffraction grating reflects the light back to the gain medium through the collimator. With this design, the primary wavelength of the light generated by the laser is dependent upon the angle of incidence of the collimated light on the diffraction grating.
In certain designs, it is desirable that the laser can be selectively and continuously tuned across a desired wavelength (or frequency) range. With a Littrow type laser, the output wavelength can be adjusted continuously by simultaneous adjustment of (i) the grating angle with respect to the incident beam, and (ii) the cavity length of the external cavity.